During one year all ankle inversion injuries seen at the acute ward of our institution were divided into grades of severity and classified according to the maximal area of tenderness at the time of clinical examination. Seven years later 648 of the subjects (91%) evaluated their ankle with the help of a questionnaire. Location of maximal tenderness at the time of injury was: lateral fibular ligaments 61%, lateral midfoot ligaments 24%, base of the fifth metatarsal/peroneal tendons 5% and combined lesions 8%. 39% were considered minor, 46% were moderate, and 15% severe. All cases followed a functional treatment protocol. Seven years post- injury 32% reported chronic complaints of pain, swelling or recurrent sprains. 72% of the subjects with residual disability reported that they were functionally impaired by their ankle - in most cases a question of not performing sports at a desired level. 4% experienced pain at rest and were severely disabled. 19% were bothered by repeated inversion injuries - 43% of these subjects felt that they could compensate by using an external ankle support. There was no correlation between the severity of the sprain as judged at the time of injury and the frequency of residual disability or between the area of maximal tenderness at the time of injury and the area of maximal pain at the time of follow-up.

The peroneal reflex time to sudden ankle inversion and the postural control of 15 athletes with functionally instable ankles were compared with 15 stable controls. A trapdoor produced sudden ankle inversion. Surface electrodes recorded electromyographic activity of the peroneal muscles. Postural sway was expressed by a transverse sway value obtained during single limb stance on a force plate. Increased postural sway was found in subjects with functional instability (p less than 0.01). This is in accordance with previous studies. Functionally instable subjects also displayed an increased peroneal reaction time (p less than 0.01) supporting the theory that functional instability is induced by a proprioceptive reflex defect. Nine of the 15 instable subjects were unilaterally instable and showed lower peroneal reaction time and postural sway values for the stable ankle, but the difference was not significant. There was a high degree of correlation between postural sway and peroneal reaction time (Spearman's rho = .92). In ten functionally instable athletes tested with and without ankle taping, it could not be verified that a reflex enhancing effect of taping occurs through stimulation of cutaneous afferents.

The reaction of 15 functionally unstable ankles to sudden inversion was described by monitoring muscle activity, joint motion, and alternation of the body center of pressure. The results were compared with those of 15 stable controls. Stable and unstable subjects showed a similar reaction pattern to sudden inversion: first, a peripheral reflex action, namely, a contraction of the peronei counteracting the ankle inverting momentum, and, then, a centrally elicited pattern, namely, a flexion of the hip, knee, and ankle relieving the vertical pressure on the ankle and producing ankle eversion. Unstable subjects did not show a defect in their central processing of afferent input. In contrast, a prolonged reaction time (median 84 msec compared with 69 msec in stable subjects) suggested a partial deafferentation of the reflex stabilization of the ankle and substantiated the theory of a proprioceptive deficit being responsible for ankle instability.

The epidemiology of sprains in the lateral ankle and foot was investigated in a prospective study at the casualty ward at Hillerød County Hospital. During one year, 766 patients were registered. The overall sprain incidence was 7/1000 person-years. The incidence was highest for young males. After the age of 40 years, the incidence was higher for women than for men. Most sprains were sustained during sport, but, with increasing age, other activities became dominant. Sixty-one percent of the lesions were located around the lateral ankle, and 24% were located on the lateral midfoot.